539 research outputs found
Ground-state phase diagram of an anisotropic spin- model on the triangular lattice
Motivated by the recent experiment on a rare-earth material YbMgGaO [Y.
Li \textit{et al.}, Phys. Rev. Lett. \textbf{115}, 167203 (2015)], which found
that the ground state of YbMgGaO is a quantum spin liquid, we study the
ground-state phase diagram of an anisotropic spin- model that was proposed
to describe YbMgGaO. Using the density-matrix renormalization group method
in combination with the exact diagonalization, we calculate a variety of
physical quantities, including the ground-state energy, the fidelity, the
entanglement entropy and spin-spin correlation functions. Our studies show that
in the quantum phase diagram there is a phase and two distinct
stripe phases. The transitions from the two stripe phases to the
phase are of the first order. However, the transition between the two stripe
phases is not the first order, which is different from its classical
counterpart. Additionally, we find no evidence for a quantum spin liquid in
this model. Our results suggest that additional terms may be also important to
model the material YbMgGaO. These findings will stimulate further
experimental and theoretical works in understanding the quantum spin liquid
ground state in YbMgGaO.Comment: minor change
Deep Reinforcement Learning for Image-to-Image Translation
Most existing Image-to-Image Translation (I2IT) methods generate images in a
single run of a deep learning (DL) model. However, designing such a single-step
model is always challenging, requiring a huge number of parameters and easily
falling into bad global minimums and overfitting. In this work, we reformulate
I2IT as a step-wise decision-making problem via deep reinforcement learning
(DRL) and propose a novel framework that performs RL-based I2IT (RL-I2IT). The
key feature in the RL-I2IT framework is to decompose a monolithic learning
process into small steps with a lightweight model to progressively transform a
source image successively to a target image. Considering that it is challenging
to handle high dimensional continuous state and action spaces in the
conventional RL framework, we introduce meta policy with a new concept Plan to
the standard Actor-Critic model, which is of a lower dimension than the
original image and can facilitate the actor to generate a tractable high
dimensional action. In the RL-I2IT framework, we also employ a task-specific
auxiliary learning strategy to stabilize the training process and improve the
performance of the corresponding task. Experiments on several I2IT tasks
demonstrate the effectiveness and robustness of the proposed method when facing
high-dimensional continuous action space problems
A novel non-homologous recombination-mediated mechanism for Escherichia coli unilateral flagellar phase variation
Flagella contribute to the virulence of bacteria through chemotaxis, adhesion to and invasion of host surfaces. Flagellar phase variation is believed to facilitate bacterial evasion of the host immune response. In this study, the flnA gene that encodes Escherichia coli H17 flagellin was examined by whole genome sequencing and genetic deletion analysis. Unilateral flagellar phase variation has been reported in E. coli H3, H47 and H17 strains, although the mechanism for phase variation in the H17 strain has not been previously understood. Analysis of phase variants indicated that the flagellar phase variation in the H17 strain was caused by the deletion of an ∼35 kb DNA region containing the flnA gene from diverse excision sites. The presence of covalently closed extrachromosomal circular forms of this excised 35 kb region was confirmed by the two-step polymerase chain reaction. The deletion and complementation test revealed that the Int1157 integrase, a tyrosine recombinase, mediates the excision of this region. Unlike most tyrosine recombinases, Int1157 is suggested to recognize diverse sites and mediate recombination between non-homologous DNA sequences. This is the first report of non-homologous recombination mediating flagellar phase variation
Multilevel Nitrogen Additions Alter Chemical Composition and Turnover of the Labile Fraction Soil Organic Matter via Effects on Vegetation and Microorganisms
Global nitrogen (N) deposition greatly impacts soil carbon sequestration. A 2- yr multiple N addition (0, 10, 20, 40, 80, and 160 kg N·ha- 1·yr- 1) experiment was conducted in alpine grassland to illustrate the mechanisms underlying the observed soil organic matter (SOM) dynamics on the Qinghai- Tibet Plateau (QTP). Labile fraction SOM (LF- SOM) fingerprints were characterized by pyrolysis- gas chromatography/tandem- mass spectrometry, and microbial functional genes (GeoChip 4.6) were analyzed in conjunction with LF- SOM fingerprints to decipher the responses of LF- SOM transformation to N additions. The significant correlations between LF- SOM and microbial biomass, between organic compounds in LF- SOM and compound degradation- related genes, and between LF- SOM and net ecosystem exchange implied LF- SOM were the main fraction utilized by microorganisms and the most sensitive fraction to N additions. The LF- SOM increased at the lowest N addition levels (10 and 20 kg N·ha- 1·yr- 1) and decreased at higher N addition levels (40 to 160 kg N·ha- 1·yr- 1), but the decrease of LF- SOM was weakened at 160 kg N·ha- 1·yr- 1 addition. The nonlinear response of LF- SOM to N additions was due to the mass balance between plant inputs and microbial degradation. Plant- derived compounds in LF- SOM were more sensitive to N addition than microbial- derived and aromatic compounds. It is predicted that when the N deposition rate increased by 10 kg N·ha- 1·yr- 1 on the QTP, carbon sequestration in the labile fraction may increase by nearly 170% compared with that under the current N deposition rate. These findings provide insight into future N deposition impacts on LF- SOM preservation on the QTP.Key PointsThe LF- SOM quantity increased at the lowest N additions (N10 and N20) and decreased from N40 to N160, but the decrease was weakened at the highest N addition (N160)Plant- derived compounds in LF- SOM were more sensitive to N addition than microbial- derived and aromatic compoundsThe organic compounds in LF- SOM were significantly correlated with compound degradation- related genesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154963/1/jgrg21637_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154963/2/jgrg21637.pd
Survival after alcohol septal ablation versus conservative therapy in obstructive hypertrophic cardiomyopathy
Background: The impact of alcohol septal ablation (ASA) on the survival of patients with drug-refractory obstructive hypertrophic cardiomyopathy (HCM) remains unresolved. The aim of this study was to compare survival after ASA vs. conservative therapy.
Methods: We studied a consecutive cohort of 274 patients with severe drug-refractory obstructive HCM, 229 in ASA group and 45 in conservative group. The primary endpoint was a composite of all-cause mortality and aborted cardiac arrest.
Results: With a median follow-up of 4.3 years, primary endpoint occurred in 13 (5.7%) patients in the ASA group, and 8 (17.8%) patients in the conservative group. The 5- and 10-year survival free from primary endpoint of the ASA group (94.5% and 93.0%, respectively) was significantly better than that of the conservative group (78.3% and 72.2%, respectively, log-rank p = 0.009). Independent determinants of primary endpoint were ASA therapy (hazard ratio [HR] 0.22; 95% confidence interval [CI] 0.08–0.60; p = 0.003) and maximal septal thickness (HR 1.14; 95% CI 1.03–1.27; p = 0.011).
Conclusions: In patients with severe drug-refractory obstructive HCM, survival after ASA is favorable and better than that of conservative therapy. ASA seems to improve survival
Effect of Langmuir monolayer of bovine serum albumin protein on the morphology of calcium carbonate
Bovine serum albumin (BSA) Langmuir monolayer, as a model of
biomineralization-associated proteins, was used to study its effect on
regulated biomineralization of calcium carbonate. The effects of the BSA
Langmuir monolayer and the concentration of the subphase solution on the
nucleation and growth processes and morphology of the calcium carbonate crystal
were investigated. The morphology and polymorphic phase of the resulting
calcium carbonate crystals were characterized by scanning electron microscopy
(SEM) and X-ray diffraction analysis (XRD). Moreover, the interaction
mechanisms of the subphase solution with the BSA Langmuir monolayer were
discussed. It was found that BSA Langmuir monolayer could be used as a template
to successfully manipulate the polymorphic phase and crystal morphology of
calcium carbonate and had obvious influence on the oriented crystallization and
growth. The final morphology or aggregation mode of the calcite crystal was
closely dependent on the concentration of calcium bicarbonate solution. It is
expected that this research would help to better understand the mechanism of
biomineralization by revealing the interactions between protein matrices and
crystallization of calcium carbonate crystal.Comment: 4 pages, 4 figure
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